Pause gameplay, highlight the stated option at the main menu, then hold (in order):
Weaponry - Select + L2 + Circle + Square + X - One hit kills Map - Right + L2 + R2 + Circle + Square + X - Complete mission Briefing - Right + L1 + L2 + Circle + X - Movie theatre
Once done (a sound will confirm correct entry), enter the Options screen and select Cheats.
